Inactivation of bacteria on fresh produce by batch wash ozone sanitation

An estimated 9.4 million illnesses are due to known foodborne pathogens every year. Consumption of fresh produce can be a risk factor for the transmission of foodborne pathogens with the potential for contamination occurring at any node in the farm to fork food pathway. Retail settings present several opportunities for cross-contamination of fresh produce to occur. Washing with the addition of a sanitizing agent is the primary intervention method or the inactivation of microorganisms potentially present on fresh produce. The present study evaluated the efficacy of a batch wash ozone sanitation system (BWOSS) for the inactivation of microorganisms on the surface of fresh produce. Three microorganisms (Escherichia coli, Listeria innocua, Salmonella Typhimurium), four types of fresh produce (tomatoes, strawberries, cilantro, romaine head lettuce), and three factors (water temperature, free chlorine, organic load) were utilized in a Central Composite Design to characterize the efficacy of the BWOSS. Multiple comparisons among microorganism type indicate significantly greater log reduction (P < 0.05) of L. innocua across all time points (4.7 logs) when compared to E. coli (4.2 logs) when all produce types were combined. Meanwhile, microbial reduction on cilantro by ozone treatment was generally lower than on all other produce types and significantly lower (P < 0.05) than cherry tomatoes at all time points. A principal component (PC) analysis was performed, and PC1 was found to represent the joint effect of water temperature, ozone, and ORP where water temperature was negatively correlated with ozone and accounted for 47% of the total variation of all of the explanatory variables. Combined with water temperature, free chlorine and organic load comprised 91% of the total variation in the BWOSS—indicating the critical nature of these variables in the ability to maintain effective ozone concentrations. Overall, this study provides a detailed analysis of the impact of critical variables on the inactivation efficacy of aqueous ozone within a BWOSS for use in retail food service establishments.